Conventional horizontal skylights suffer from poor sunlight collection when the sun is low in the sky, i.e., when the sun's elevation angle is small. This poor low-sun-elevation angle performance leads to poor lighting in the wintertime in most moderate latitudes, and to poor lighting early and late in the day in all locations. Previous attempts to solve this problem have sometimes used expensive tracking reflectors above the skylight penetration into the building, or sometimes used fixed reflectors or prismatic lenses above the skylight penetration with less than adequate performance.
Conventional horizontal skylights also suffer from excess sunlight collection when the sun is high in the sky, i.e., when the sun's elevation angle is large. This excess sunlight collection during summer months near solar noon increases solar heat gain with corresponding increases in air conditioning loads and costs. Previous attempts to solve this problem have sometimes used expensive blinds and baffles to block some of the excess sunlight collection with less than satisfactory performance, reliability, and cost.
Conventional skylights mounted on conventional curbs suffer from low light collection when the sun is low in the sky, i.e., when the sun's elevation angle is small. For such prior-art skylights, only small amounts of sunlight from low sun elevation angles can be collected by the skylight due to the high incidence angle of the solar rays onto the horizontal plane of the skylight. This defect in prior-art skylights severely limits light collection early and late in the day, and all day long in mid-winter months for high latitudes, when the sun never gets high in elevation angle. Conventional skylights also suffer from excess light collection and solar heat gain in the hours around solar noon in the summer, inflating air-conditioning usage and cost.
Conventional skylights mounted on conventional curbs also suffer from structural weaknesses, especially after the skylight material has aged and embrittled in the outdoor environment, sometimes leading to workers being killed or injured due to falls through such skylights. The weakness of previous skylights has also led to hail penetration into the building below, causing damage to the contents and significant expense for repairs and replacement. Previous attempts to solve this structural weakness problem include adding protective metal grids or cages either over or under such skylights for fall protection, but such grids or cages are expensive and block a considerable amount of light. Other previous attempts to solve this problem include making the skylight dome material thicker, but this requires more material usage and thus adds both expense and weight to the skylight.
An embodiment of the current subject matter uses a relatively tall dome (the inner dome) with an innovative light-diffusing partial cap (the outer dome) over the inner dome where the partial cap extends part of the way down the sides of the dome, but not all the way down the sides of the dome, and the outer dome is bonded to the sides of the inner dome. The partial cap intercepts a substantial amount of the low sun elevation angle light and, by diffusing at least a portion of such light downward, is thereby able to deliver a significant fraction of such low sun elevation angle light into the building below for illumination.
Most low sun elevation angle light striking the inner dome below the level of the partial cap hits the inner dome at a low enough height that it will enter the building and it's not necessary to diffuse it to make a portion of it enter the building. If, instead of the cap, there was an outer diffusing dome covering the entire inner dome, (a common construction in the skylight industry), then low sun elevation angle light striking the lower part of the skylight would suffer a loss in transmittance when it passed through the outer diffusing dome that it doesn't suffer when there's a partial cap and the lower part of the inner dome isn't covered by an outer diffusing dome. Thus, if there was an outer diffusing dome covering the entire inner dome, the collection of low sun elevation angle light would thus be significantly reduced compared to the partial cap covering the top and part of sides of the inner dome.
The partial cap also reduces the collection of high sun elevation light through the part of the dome covered by the cap by reducing transmittance through the top of the dome and by scattering high sun elevation light so that its effective sun elevation angle is reduced and some of it is scattered out of the dome and doesn't make it into the building.
The partial cap also strengthens the dome for fall protection and for hail resistance, at only a fraction of the cost of making the entire dome thicker. Therefore, the disclosed subject matter solves two critical problems in conventional skylights, improving low sun elevation angle sunlight collection and strengthening the skylight for fall protection and hail impact resistance.
The disclosed subject matter can take many different forms. The basic skylight dome can be many different sizes and shapes, and the cap for the dome can likewise be many different sizes and shapes and extents. The disclosed subject matter can also be tailored for a variety of applications, from big-box stores to offices to residences.
The disclosed subject matter is a unique new skylight, using a relatively tall transparent or translucent dome with a partial cap of light-diffusing material to both collect more low sun elevation angle sunlight and to also strengthen the dome for personnel safety, protection of building contents from weather damage, and product longevity. The disclosed subject matter also reduces solar heat gain and associated air-conditioning costs during the mid-day hours in summertime.
The present subject matter uses a relatively tall diffusely transmitting dome to collect low sun elevation light, with a thicker shade near the top of the dome to block high sun elevation light, thereby solving both problems by both increasing inadequate sunlight collection during low sun elevation periods and also by decreasing excess sunlight collection during high sun elevation periods. The present subject matter solves both problems in a totally passive manner, requiring no moving parts and no seasonal change in configuration of the skylight. Therefore, the present subject matter represents a simple, reliable, cost-effective solution to two major problems for horizontal skylights.
This subject matter includes at least one skylight dome with relatively tall partially vertical sides comprising partially transparent material which diffuses the transmitted light, and at least one mostly opaque sun shade near the top of the relatively tall partially vertical sides. The partially vertical sides are able to better intercept sunlight from low sun elevation angles, in contrast to conventional horizontal skylights which are less well able to intercept such low-sun-elevation-angle light. The thicker shaped portion is more opaque because of the thickness than the vertical walls and is able to block sunlight from high sun elevation angles to prevent such sunlight from entering the building below the dome. By enhancing the collection of low-sun-elevation-angle light with the thicker and thus more opaque to surface, the subject matter improves the daylighting performance of the skylight early and late in the day year around, and all day in the winter months of the year. By reducing the collection of high-sun-elevation-angle light, the subject matter reduces the solar heat gain near solar noon in the summer months, thereby reducing air conditioning loads and related costs for equipment and operating energy. The simple passive configuration of the subject matter, with no moving parts and no operational complexity, ensures high reliability and low maintenance.
The disclosed subject matter uses a relatively tall dome (the inner dome) with an innovative light-diffusing partial cap (the outer dome) over the inner dome where the partial cap extends part of the way down the sides of the dome, but not all the way down the sides of the dome, and the outer dome is bonded to the sides of the inner dome. The partial cap intercepts a substantial amount of the low sun elevation angle light and, by diffusing at least a portion of such light downward, is thereby able to deliver a significant fraction of such low sun elevation angle light into the building below for illumination.
Most low sun elevation angle light striking the inner dome below the level of the partial cap hits the inner dome at a low enough height that it will enter the building and it's not necessary to diffuse it to make a portion of it enter the building. If, instead of the cap, there was an outer diffusing dome covering the entire inner dome, (a common construction in the skylight industry), then low sun elevation angle light striking the lower part of the skylight would suffer a loss in transmittance when it passed through the outer diffusing dome that it doesn't suffer when there's a partial cap and the lower part of the inner dome isn't covered by an outer diffusing dome. Thus, if there was an outer diffusing dome covering the entire inner dome, the collection of low sun elevation angle light would thus be significantly reduced compared to the partial cap covering the top and part of sides of the inner dome.
These and many other advantages of the present subject matter will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.